This disclosure relates to methods and apparatus for controlling the movement or position of a hydraulic component using one or more of a plurality of fluid supplies. The hydraulic component may be a piston, a ram, a plunger, a valve, among other components.
A hydraulic circuit 200 that may be part of a blowout preventer is illustrated in FIG. 1. Typically in blowout preventers, pressurized hydraulic fluid is employed to close or open shearing rams or gate valves. In the example shown in FIG. 1, the pressurized hydraulic fluid acts on a piston of a hydraulic component 212, for example for controlling a gate valve. Moreover, in blowout preventers, multiple control systems may be used to control the same hydraulic component. For example, the multiple control systems may be located in different control pods of the blowout preventer. In the example shown in FIG. 1, each control pod may include an independently pressurized fluid supply 214 to control the hydraulic component 212.
For ensuring proper functioning of the hydraulic component, it is important that pressurized fluid flowing from one fluid supply 214 is routed toward the hydraulic component 212. In particular, the pressurized fluid shall not inadvertently crossflow into another fluid supply 214 configured to also control the same hydraulic component 212. Shuttle valves 220 may be used for this purpose. In cases where only one control pod is active at a time, shuttle valves 220 may properly route the pressurized fluid from the one fluid supply 214 located in the active control pod toward the hydraulic component 212. However, the shuttle valves 220 may not be sufficient to prevent crossflow between two fluid supplies 214 that are active at the same time.
Additionally, the pressurized fluid shall not be inadvertently vented into a venting port, such as into venting port 226 when one of the fluid supplies 214 is active. However, a backflow path through the venting port 226 may be provided for discharging hydraulic fluid escaping from the hydraulic component 212 when the hydraulic component is actuated in a reversed direction. In the example shown in FIG. 1, the piston of the hydraulic component 212 may be retracted by activating the fluid supply 215, and by discharging the hydraulic fluid in the extend chamber of the hydraulic component 212 through the venting port 226. To adequately control the discharge of hydraulic fluid via the venting port 226, a pilot-to-open check valve 266 may be configured to permit the discharge of the hydraulic fluid from the extend chamber of the hydraulic component 212 through the venting port 226 only when the piston of the hydraulic component 212 is being retracted. The check valve 266 is only opened by fluid pressure in a pilot line 224. Conversely, a pilot-to-open check valve 267 may be configured to permit the discharge of the hydraulic fluid from the retract chamber of the hydraulic component 212 through the venting port 227 only when the piston of the hydraulic component 212 is being extended. The check valve 267 is only opened by fluid pressure in a pilot line 225. Therefore, at any time during operation of the hydraulic circuit 200, the hydraulic fluid in either the pilot line 224 or the pilot line 225 remains trapped at a high pressure. When a blowout preventer operating in the subsea environment is retrieved to the surface, the pressure differential between the fluid trapped in one of the pilot lines and the environment of the blowout preventer may reach an excessive level, endangering the safety of personnel working on the retrieved blowout preventer.
Thus, there is a continuing need in the art for methods and apparatus for controlling a movable component, in particular, a component of a blowout preventer, using one or more of a plurality of fluid supplies. These methods and apparatus preferably permit two or more of the plurality of fluid supplies to be active at the same time while reducing crossflow between the fluid supplies. Also, these methods and apparatus can mitigate the risk of trapping hydraulic fluid at high pressure. For example, these methods and apparatus can be used on blowout preventers operated in the subsea environment. In such cases, these methods and apparatus can mitigate the risk of reaching excessive pressure differential in the controlling apparatus or elsewhere in the blowout preventer during the retrieval of the blowout preventer to the surface.